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Brain anatomy of esophagus-‐less Osedax (Siboglinidae) and organisa9on of the canonical for annelids supraesophageal commissures
RESULTS. The brain anatomy of female Osedax priapus and Osedax ‘‘yellow collar’’ were reconstructed based on histology and 3D modeling (Figs. C-‐E). In both species there is the same organiza9on of the brain. Osedax has a ventral intraepidermal brain, consis9ng of a large neuropile (Figs. F-‐K) that ventrally and laterally is covered by densely packed perikarya (Fig. L). The neuropile contains a number of transverse commissures as well as longitudinal and diagonal neurite bundles (Figs. F, J, K, M). In the posteriomost brain are found a dorsal and a ventral commissural bundle with inter-‐decussa9ng fibers, both of which connect with the ventral nerve cords (Figs. F, J, M). A dorsal and a ventral neurite bundle innerva9ng each palp originate from median commissures (diagonal and transverse) and two anterior commissures of the neuropile, respec9vely (Figs. F, G, N, P). The connec9on of these commissures to the ventral cords cannot be traced, due to the laterally disguising dense neuropile, also complica9ng the homology assessment of Osedax brain characters. There are three main accumula9ons of perikarya: posterior, anterior elongated perikarya and anterior round perikarya (Figs. (Fig.H, L, M-‐P).
Nadezhda N. Rimskaya-‐Korsakova1, Greg W. Rouse2, Katrine Worsaae3 1Department of Invertebrate Zoology, Lomonosov Moscow State University, Leninskie Gory 1-‐12, Moscow, 119234, Russia, rimskaya-‐[email protected] 2Scripps Ins9tu9on of Oceanography, 9500 Gilman Drive, La Jolla, California 92093-‐0202, USA, 3Marine Biological Sec9on, Department of Biology, University of Copenhagen, Universitetsparken 4, DK-‐2100 Copenhagen, Denmark,
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C D E
F G H I
J K L
M N O P
Fig. A. O.“orange-‐collar”, sister to O.”yellow-‐collar”(Vrijenhoek etal.,2009)
Figs. C-‐E. Brain loca9on and arrangement of peripheral neurite bundles origina9ng from the brain of O.“yellow-‐collar”. Overviews of the anterior part of the tubeworm: lee (B), posterior view (C), and right (D). Transparent grey – four palps, transparent orange -‐ body and oviduct, red – peripheral nerves (of anterior trunk, oviduct, palps), white – neuropile of the brain, grey – accumula9ons of perikarya of the brain, green – large cells, presumably also perikarya. Scale bar 20 μm.
Fig. F. Schema9c drawing of the Osedax “yellow-‐collar” brain, based on 3d reconstruc9ons. Lehers in boxes show levels at which the histological sec9ons were made (see Figs. L-‐O).
posterior commissure
anterior commissures
longitudinal nerve bundles
dorsal palp nerves 1,2
oviduct nerve
dorso-‐lateral nerve
ventral nerve cord
ventral palp nerves 1,2
oviduct nerve
dorso-‐lateral nerve ventral
nerve cord
palp nerves
posterior brain commissure
median commissures
Fig. G. Main commissures and origin of the peripheral nerves in the brain of O. “yellow-‐collar”, dorsal view of the 3d model, scale bar 20 μm.
Fig. H. Main commissures and perikarya accumula9ons of the brain of O. “yellow-‐collar”, dorsal view of the 3d model, scale bar 20 μm.
posterior perikarya
anterior elongated perikarya
anterior round perikarya
Fig. I. 13 pairs of large perikarya among anterior round perikarya, as well as three pairs of huge cells, presumably perikarya, scale bar 50 μm.
Fig. J. Main nerve bundles of the brain of O. “yellow-‐collar”, dorsal view of the 3d model, scale bar 10 μm.
Fig. K. Main nerve bundles of the brain of O. “yellow-‐collar”, right lateral view of the 3d model, scale bar 10 μm. Fig. L. Main nerve bundles and perikarya accumula9ons of the brain of O. “yellow-‐collar”, right lateral view of the 3d model, scale bar 10 μm.
huge perikarya
large perikarya
anterior elongated perikarya
posterior perikarya anterior
round perikarya
longitudinal nerve bundles
longitudinal nerve bundles
anterior brain commissures
posterior brain commissures
ventral nerve cord
ventral nerve cord
subepidermal neurite bundles
anterior brain commissures
ventral network of nerve bundles
ventral network of nerve bundles
posterior brain commissures
anterior round perikarya
posterior perikarya
large perikaryon
large perikaryon ventral network of
nerve bundles
anterior brain commissure
Roots of dorsal palp
nerve
anterior elongated perikarya
anterior round perikarya
anterior brain commissure
longitudinal nerve bundles
posterior perikarya
anterior round perikarya
Roots of ventral palp
nerve
anterior elongated perikarya
longitudinal nerve bundles
longitudinal nerve bundles
protec9ve cu9cular shield
Fig. M. Histological sec9on at the level of the posterior brain commissure in O. “yellow-‐collar”. The level showed at Fig. F, scale bar 10 μm.
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M
N
O
Figs. N, O. Histological sec9ons of the brain of O. “yellow-‐collar” at the level of the anterior brain commissures: dorsal (M) and ventral (N) ones. The level showed at Fig. F, scale bar 10 μm.
Fig. P. Histological sec9on of O. “yellow-‐collar” brain at the level of the roots of the posterior ventral palp nerves. Level showed at Fig. F, scale bar 10 μm.
INTRODUCTION. Gutless siboglinid tubeworms (frenulates, Osedax, see Fig. A, Sclerolinum and ves9men9ferans) relying their nutri9on on bacterial endosymbionts is an annelid group of uncertain phylogene9c posi9on. Orrhage and Müller compared the brains (a.k.a. supraesophageal ganglion) of a range of annelids and showed the general presence of 4 transverse commissures (though with different level of integra9on in the adult stage), connec9ng through their roots and circumesophageal connec9ves to the ventral nerve cords. Hitherto, brains of siboglinids remain understudied, except for the brain of the large-‐sized Ves9men9fera, excep9onally shown to cons9tute a fusion of both the supra-‐ and subesophageal ganglia (Fig. B). Studies of other siboglinids are required for tracing the ancestral state of brain and substructures.
ACKNOWLEDGEMENTS. Organizers of the IPC12Cardiff. Dr. Alexandra Kerbl for a great assistance and pa9ence to teach NNR-‐K in 3d modeling in Imaris soeware. The histological and microscopical surveys were done with support by the Russian Scien9fic Research (#14-‐14-‐00262), the 3D-‐modeling was supported by the Russian Scien9fic Fund (#14-‐50-‐00029), the visits f the University of Copenhagen are realized because of MARS travel award (2015).
«brain»
palp nervestentacularnerves
supraenteralcommissure
subenteralcommissure
ventral root
dorsal root
circumesophageal connectives
supraesophageal ganglion(brain)
gut rudiment
subesophageal ganglion
dorsalcommissure
longitudinal nerve bundlesgut
Fig. B. Hypothe9cal “origin” of the brain of ves9men9feran tubeworms from annelid one (Rimskaya-‐Korsakova etal., 2012)
B
median commissures:
